The tutor gives an example of using Excel’s Goal Seek.

Example:

Solve lnx + 15= 0.25x

Solution:

1. Select a cell (let’s imagine e3), then name it X (or whatever name you prefer. See how to name a cell in my post here.)
2. Select another cell (let’s imagine d3), then enter the formula =0.25*X
3. Select yet another cell (let’s imagine c3), then enter =ln(X) + 15
4. Select yet another cell (let’s imagine b3), then enter =c3 – d3
5. Now, select the Data pane (it’s one of those across the top, along with Home, Page Layout, Formulas, etc). When you do, you’ll see a Data Tools area that will include What-If Analysis. Click that, then Goal Seek…
6. A dialogue will open. In our case, we want b3 to have value 0. So for Set Cell we can just select b3.
7. In the box To Value, we enter 0.
8. Our variable is in the cell named X. In the By Changing Cell box we enter X, e3, or simply select e3.
9. Clicking OK, we see the cells change as the answer evolves. Then a dialogue called Goal Seek Status opens, telling the solution if one is found. When you click OK, the solution (if found) will be applied to the relevant cells.
10. In this case, it seems that X becomes 77.39566, giving b3 a value of 1.69e-5 which equals 0.0000169. Excel deems this value close enough to 0, and I tend to agree:)

HTH:)

Source:

Microsoft Excel 5.0 User’s Guide. Microsoft Corporation, 1993.

Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.